1. Field of the Invention
This invention is in the field of medicinal chemistry. In particular, the invention relates to protease inhibitors for coronaviruses and SARS-CoV, or picornaviruses. The invention also relates to the use of these protease inhibitors for ameliorating or treating disease that was caused by coronaviruses and SARS-CoV, as well as picornaviruses.
2. Prior Art
The causative pathogen of severe acute respiratory syndrome (SARS) has been identified as a virus of the coronavirus family (Peiris J. et al. Lancet, 2003, 361: 1319-1325). Coronaviruses are positive-stranded RNA viruses with large genome sizes and are known to be responsible for diseases in animals and in humans. There are two coronaviruses, HCV OC43 and HCV 229E, that are known to be the cause of some common colds. The molecular biology of these coronaviruses has been studies and there is a good understanding of the structure and function of the genes and proteins of these viruses (Lai, M. M. C. and Cavanagh, D. Adv. Virus Res. 1997, 48: 1-100). Coronaviruses are known to encode several proteases that process the virus proteins and these proteases are essential for the replication of the viruses (Ziebuhr J. et al. J. Gen. Virol. 2000, 81: 853-79). These proteases have been found to be cysteine proteases, including PL1pro and PL2pro that are papain-like protease, and are analogous to the foot and mouth disease virus leader protease, Lpro, as well as the main 3CLpro that is a chymotrypsin-like protease, and is analogous to the main picornavirus protease, 3Cpro. The conservation of substrate specificities among the main proteases 3CLpro of coronaviruses has been reported, with LQS or LQA as the preferred P2-P1-P1′ sequences (Hegyi A. and Ziebuhr J. J. Gen. Virol. 2002, 83: 595-9; and Hegyi, A. et al. J. Gen. Virol. 2002, 83: 581-593). The genome of the new coronavirus that cause severe acute respiratory syndrome (SARS-CoV) has been determined by several groups (Ksiazek, T. et al. N. Engl. J. Med. 2003, 348: 1953-1966; and Drosten, C. et al. N. Engl. J. Med. 2003, 348: 1967-76). It is reported that although the overall gene products of ORF1a are poorly conserved among different coronaviruses, the protease sequences are the exceptions. The predicted gene product of ORF1a of SARs-CoV appears to contain one PLPpro domain. The 3CLpro catalytic histidine and cysteine residue are fully conserved among all coronaviruses including SARS-CoV (His3281 and Cys3385) (Rota P. et al., Scienceexpress, 2003, 300: 1394-1399). In addition, it is reported that the replicase 1a and 1b ORFs of SARS-CoV occupy 21.2 kb of the SARS virus genome. The genes encode a number of proteins that are produced by proteolytic cleavage of a large polyprotein, which is conserved in both length and amino acid sequence to other coronavirus replicase proteins (Marra M. A. et al., Scienceexpress, 2003, 300: 1399-1404). These results suggested that the protease of SARS-CoV should process the viral protein similar to other coronaviruses.
The proteases of coronaviruses are essential for the processing of viral proteins and replication of the viruses. It has been reported that a cysteine protease inhibitor E64d inhibited the posttranslational processing of viral protein and the replication of the viruses (Kim, J. C. et al. Virology, 1995, 208: 1-8). Therefore the design and synthesis of protease inhibitors of SARS-CoV, and coronaviruses, could lead to effective treatment for SARS, as well as effective treatment for other disease that were caused by the coronaviruses in animals and humans.
The protease inhibitor of SARS-CoV and coronaviruses can be designed based on the known conservation of substrate sequence of coronaviruses, and preferably using a dipeptide scaffold. The dipeptide scaffold approach has been used successful in the design of potent and efficacious inhibitors of caspases, another class of cysteine protease important for apoptosis (U.S. Pat. No. 6,184,210). The dipeptide scaffold can be LQ, which is conserved among the main proteases 3CLpro of coronaviruses. The dipeptide scaffold also can be RG or RA, which are preferred and conserved for the PL1pro of coronaviruses (Dong, S., Baker, S. C. Virology, 1994, 204: 541-9; and Hughes S. A. et al. J. Virol. 1995, 69: 809-13).
Picornaviruses, another class of RNA viruses, also encode a viral 3C protease for the processing and release of viral proteins, which are essential for the replication of the viruses. The Picornaviruses family are divided into 6 subgroups with similar genetic organization and translation strategies. These subgroups include several important human and veterinary pathogens, such as poliovirus and coxsackievirus (Enterovirus), foot-and mouth disease virus (Aphthovirus), encephalomyocarditis virus (Cardiovirus), hepatitis A virus (Hepatovirus), and human rhinoviruses (Rhinovirus). The crystal structures of several picornavirus 3C proteases have been determined, including type 14 human rhinovirus (Matthews, D. A. et al. Cell, 1994, 77: 761-771), hepatitis A (Allaire, M. et al. Nature (London), 1994, 369: 72-76) and poliovirus (Mosimann, S. C. et al. J. Mol. Biol. 1997, 273: 1032-1047). Picornaviral 3C proteases are a unique class of enzymes with an unusual specificity for Gln-Gly cleavage of its substrates (Matthews, D. A et al. Proc. Natl. Acad. Sci. USA, 1999, 96: 11000-11007). This specificity for Gln-Gly cleavage of substrates is similar to that of the main protease 3CLpro (Mpro) of coronaviruses (Anand, Science, 2003, 300: 1763-1767). Therefore it is expected that protease inhibitor of SARS-CoV and coronaviruses of this invention also should be active as inhibitors of picornaviral 3C proteases, and will be useful for the treatment of diseases that were caused by picornaviruses.